Radiant and convection heat furnace



Oct. 4, 1932. A. MEKLER RADIANT AND CONVECTION HEAT FURNACE Filed April 29. 1929 Patented Oct. 4, 1932 PATENT YOFFYICE.

UNITED STATES LEV A. MEKLER, OI CHICAGO, ILLINOIS, ASSIGNOR TO UNIVERSAL OIL PROD UCTS COH- PANY, OF CHICAGO, ILLINOIS, A CORPORATION OF SOUTH DAKOTA Ramnd: AND convaorron HEAT summon Application filed April 29,

The invention particularly comprises two 1 banks of heating tubes, one heated by convection and radiation from the gases, and the other heated by radiation from the flame, the gases and the surrounding refractories. The convection heated tubes are disposed in a portion of th furnace where the fullest advantage of all the convection heat of the furnace may be had. The fuel is burned in a large combustion chamber separated from the convection tube chamber by a wall extending the whole length of the furnace. The products of combustion generated by the burners located in the end wall of the combustion chamber enter the convection tube chamber over the top of the separating wall. Except for a minimum amount of radiation from the brickwork above the tube bank, the convection tubes are protected from the radiant heat in the combustion chamber proper and substantially all the heat is put into the fluid by convection and radiation from the gases passing over the tubes.

The fluid then passes to the second bank of tubes comprising the radiant heat section. It is to the disposition of the tubes in this section that the present invention chiefly relates. The tubes in the radiant section are so disposed that a constantly decreasing rate of heating is obtained after the fluid leaves the convection section. In a preferred embodiment of this invention a series of rows of tubes are disposed adjacent the ceiling of the combustion chamber, and in addition a series of rows of tubes are positioned adjacent one end wall opposite the battle wall which sep arates the combustion chamber from the convection chamber. The fluid is passed through the above mentioned tubes in such a. manner as to absorb less and less radiant heat as the fluid continues its travel. More particularly,

"0nd row of Wall tubes.

1929. Serial No, 358,999.

the fluid enters the lowest row of the ceiling section of tubes, that is, the row of the ceiling tubes closest to the radiant heat sources and parallel to the floor of the furnace. It is apparent that the heat absorption of these tubes is the front row of the wall tubes which have a rate of absorption somewhat lower than the rate of the first mentioned tubes. The fluid then continues its travel through the second row of wall tubes and has still a smaller rate of absorption. Th fluid next passes through the second row of ceiling or roof tubes which, due to the fact that they are partially shielded from direct radiation by the lowest row, and also shielded from the indirect radiation of the roof itself by the third row of tubes, has a lower rate of heat absorption than the sec- The third row of roof tubes next carry the fluid wherein it absorbs comparatively little heat in comparison to the absorption obtained in the preceding rows.

Another important object of the invention is to provide, by the disposition of the tubes as above described, a thermal siphon of the gases within the combustion chamber. The natural tendency of the hot gases is to rise. On rising they meet the relatively cool surfaces of the ceiling or roof tubes, and are considerably cooled by the contact therewith, become heavier and begin to settle to the bottom. The location of the wall tubes facilitates the circulation of the gases. These gases will circulate starting from the floor, the major portion ascending along the dividing wall, aforementioned, which is very hot, and then descending along the cool wall adj acent. and cooled by, the aforementioned wall tubes.

Other and further important objects of the invention will be apparent from the accompanying drawing and following description.

In the drawing a sectional view of the furnace is shown, particularly illustrating the disposition of the tubes. the path of the fluid being shown diagrammatically.

Referring more in detail to the drawing, 1 indicates generally the combustion chamber of a furnace, designated as a whole 2. The walls of the said furnace are of the accep ed highest. The fluid then passes to the suspended wall construction, being built up of an outer wall of ordinary brick 3, a cooling air space 4, and an inner wall of refractory brick or the like 5. In practice, the provision of theair space serves the double purpose of cooling tlie'refractories and preheating the air passed therethrough, which air is laterutilizedin the combustion process.

The" roof of the combustion chamber 1 comprises a series of suspended refractory bricks 7, the same being ysupported by suitable steelwork 8, which in turn is supported primarily by a pluralityof upstanding I beams 9.

A tunnel structure'10 is positioned at the lower front portion of the furnace 2, comprising a group of three horizontally disposed tunnels 11, 12 and 13, being the upper, middle and lower tunnelrespectively. The above mentioned tunnels communicate at one end with the combustion chamber and at the other with a compartment 14 provided at the front end of the structure 10. Positioned in an opening 15 in the front wall of the compartment 14 is a conventional oil-or gas burner 16, the nozzle '17 of which extends into the central tunnel 12, wherein combustion takes place. Air for combustion issupplied through a duct 18 which preferably traverses the length of the furnace 2, and communicates with the compartment 14. A damper 19 may be provided at the point of communication of the duct 18 and compartment 14 and controls the air admitted to the" combustion chamber.

The tunnels 11 and 13 are provided with suitable dampers 20 and 21, respectively. The purpose and use of the tunnel 11 is to admit air to the combustion chamber, as is fully explained in my co-filed application entitled Luminosity control in a radiant heat furnace.

A bridge or baflle wall 22 is positioned in the combustion chamber and is disposed oppositely to the tunnels 11, 12 and 13, and runs the length of the said chamber. A space 23 is provided between the Wall 22 and the rear wall of the furnace. The flue gases are adapted to pass over the wall 22 and downwardly through the'space 23 to a conduit 24 which leads to a stack 25. The floor of the combustion chamber proper is constructed of a refractory brick or the like 26. The said brick beinglaid irregularly as shown at 27 asare" the bricks 28 onthe inner side of the wall 22. The provision of the irregularly placed bricks 27 and 28 is to retard or cause a dragging action'ofthe gases of combustion in addition to providing a refractory surface of greater area. w

A plurality of tubes 29 are positioned in .the space 23 behind-'theiwall 22'andare disposed parallel to the lsaid wall. This group of tubes will hereinafter be referred to as the convection section. Another group of tubes is positioned adjacent the roof and front wall of the combustion chamber. This group will be refered to as a whole as the radiant section and will be designated by rows as follows: The lowest row of roof-tubes 30; the outside row of Wall "tubes 31;'the inside row of wall tubes 32; the second row of roof tubes 33; and the top row of roof tubes 34.

In the heating of fluids, particularly in the oil cracking art, the charging stock is admitted to the bottom portion of the convection section, as shown diagrammatically at 35. The oil is heated in this group of tubes by the convection and radiant heat of the hot gases from the combustion chamber lthat pass over the wall 22 and down through the space 23. As the oil is heated is rises in the convection tubes and flows counter-current to the flow of the convection gases. The direction of flow of the oil from tube to tube isshown diagrammatically by the tracer lines 36. The oil then passes to the end tube 37 of the top row 34 of the'radiant section, thence to the end tube 38 of the middle row 33 and then to the end tube 39 of the lowest row 30. It is apparent that the end tubes 37, 38 and 39 are exposed to the radiant heat of the refractories of the upper rear wall 40, hence instead of mechanically shielding the end tubes 38 and 37, as is usually done, the end tubes are fed with comparatively cool oil from the convection section. Therefore, the tendency for these end tubes to become overheated is eliminated. The oil then proceeds to flow through the lowest row of roof tubes 30 in the direction indicated by the lines 36.

It can be readily seen that this said row of tubes is directly exposed to the sources of radiant heat at the greatest angle of incidence and in addition each tube in this particular row is progressively subjected to substantially less and less heat, due to its relative position with respect to the sources of radiant heat, i. e., the flame, wall refractories, and the radiant heat given off by the gases. The oil then passes to the outside row of wall tubes 31, also directly exposed to the sources of radiant heat, but due to the relative position of the said tubes the angle of incidence with respect to the sources of radiant heat is smaller than the tubes of row 30. This is likewise true for each tube in the row 31, that is, as the oil descends in the row of tubes 31, the angle of incidence of each successive tube becomes less and less, and hence the rate of heat absorption proportionately. decreases. The oil then ascends upwardly through the row 32, which is partially shielded from direct radiation by the row 31 andalso receives indirect radiation fromthe refractories 5. The oil then passes to the middle rowof ceiling tubes 33 where, due to the shielding effect of the row 30 and therow 34, from direct and indirect radiation, respectively, from the primary sources of radiant heat and the indi-- and 33, the principal source of radiant heat being the ceiling refractories. The oil is thus heated in a progressively decreasing manner wherein the tubes exposed to the highest heat carries the relatively coolest oil, and as the oil is heated it passes to portions of the radiant section subjected to a lower rate of heat input. This arrangement obviously reduces the possibility of overheating any one portion of the heating elements to a minimum, and in the cracking of oil particularly, is a most eflicient means of heating.

Although the invention refers primarily to the cracking of oil, I do not wish to be limited thereto, for the method will apply'equally well wherever it may be desired to heat any fluid at a progressively decreasing rate.

By this arrangement of the tubes a thermal siphon of the gases within the chamber is induced. The hot gases given off by the flame issuing from the tunnel 12 will naturally rise, particularly along the wall 22 which is very hot, whereupon they encounter the cool surfaces of the roof bank of the radiant section of tubes and are considerably cooled by the contact therewith. Upon cooling thusly they become heavier and begin to settle to the bottom. In their downward travel they descend in contact with the wall tubes 31 and 32 and are further cooled, until they come to the tunnel 12 where they are again heated by the flame issuing therefrom, and so on. Hence, a circulation and a recirculation of the gases within the combustion chamber is brought about.

It is apparent that herein is provided a means and method of disposing tubes in a combination radiant and convection heat furnace, and of passing liquid therethrough which not only lengthens the life of the equipment, but heats the fluid more eflicientlv. This latter feature is particularly true with respect to the cracking of oil, since as the temperature of the o l increases. particularlv above 800 F., the oil is susceptible to a greater extent to thermal decomposition on overheating. By the arrangement hereinbefore described overheating is practically impossible.

I claim as my invention:

1. A, method of heating by radiant heat a fluid in a series of rows of tubes disposed adcent the roof and one wall of the combustion chamber of a furnace, comprising passing the coldest portion of the fluid through the row of roof tubes exposed to the most intense radiant heat,.then passing the fluid to the row of wall tubes most exposed to radiant heat, thence passing the fluid through the row of wall tubes least exposed to radiant heat,

7 then passing the fluid through the row of roof tubes less exposed to radiant heat than the first row, and then passing the fluid through the row ofroof tubes least exposed to radiant heat.

2. A heat transfer apparatus, comprising a combustion chamber, a plurality of rows of tubes disposed along the roof and one wall or the combustion chamber, a connection between the lowest row of roof tubes and the outer row of wall tubes, a connection between the outer and inner row of wall tubes, a connection between the inner row of wall tubes and the second row of roof tubes and a connection between the second row of roof tubes and the top row of roof tubes, all the tubes being adapted tocarry a fluid to be heated.

3. A heating furnace,includingincombination a combustion chamber provided with a heat inlet, a bafile wall oppositely disposed from the heat inlet, a bank of convection tubes positioned in a convection chamber provided between the baffle wall and the end of the combustion chamber, a plurality of rows of tubes disposed adjacent the roof and one wall of the combustion chamber, a connection between the lowest row of roof tubes and the outer row of wall tubes, a connection. between the outer and inner row of wall tubes, a connection between the inner row of wall tubes and the second row of roof tubes, a connection between the latter row and the top row of roof tubes, and a connection between the convection bank and the lowest row of roof tubes, all of the said tubes being adapted to carry a fluid to be heated.

4. A method of heating a fluid by radiant heat in a series of rows of tubes disposed adjacent the roof and one wall of the combustion chamber of a furnace, comprising first passing the fluid through a first row of roof tubes exposed to the most intense radiant heat, then passing the fluid through a row of wall tubes less exposed to radiant heat than said firstrow, and subsequently passing the fluid through a second row of roof tubes still less exposed to radiant heat.

5. A method of heating a fluid by radiant heat in aseries of rows of tubes disposed adjacent the roof and one wall of the combustion chamber of a furnace, comprising first passing the fluid through a first row of roof tubes exposed to the most intense radiant heat, thenpassing the fluid through the row of wall tubes most exposed to radiant heat, thence passing the fluid through snow of wall tubes less exposed to radiant heat than the first-mentioned row of wall tubes, and subsequently passing the fluid through a second row of roof tubes less exposed to radiant heat than said first row of roof tubes.

6. A heat transferapparatus comprising a furnace, a plurality of. rows of roof tubes disposed along the ,roof of the furnace, wall tubes disposed along a wall of the furnace, a

eonnection betweenthe lower row of roof tubes and -ne end of the wall tubes, and a.

' connection between the other end of the wall tubes and the second row of roof tubes, all the tubesbeing adapted 'to carry a fluid to be heated.

V 7. A'heat transferhapparatus comprising a I furnac e,ap1ura1ity of-rows of tubes disposed along :the roof and one wall of the furnace, a

connection between'thelower row of roof tubes and the outer row of wall tubes, a connection between the 'outenand inner rows of wall tubes, and a'conneetio'n between the inner row of Wall tubes and the second row of roof tubes, vall the tubes being adapted to carry a fluid to be heated.

In testimony whereof I aflix my signature.

LEV A. MEKLER. 

